With the advancement of on-demand printing, there has been earnestly desired to develop a toner and a developer which can meet the requirements of both high speed and high-quality image. Especially in a high-speed machine, an excellent fixing ability is required because the heat conduction time is short. Recently, there has been also necessity to carry out label printing or printing on a thick paper such as a hard cover of a book. From these viewpoints, improvement in the fixing ability of a toner has been also an important problem to be solved.
On the other hand, from the viewpoint of obtaining high-quality image, there has been proposed the use of a composite oxide as a black colorant as a substitute material for a carbon black having a low resistance (see Japanese Patent Laid-Open No. 2000-10344 (corresponding to U.S. Pat. No. 6,130,017), Japanese Patent Laid-Open No. Hei 9-25126, Japanese Patent Laid-Open No. 2002-196528 (corresponding to U.S. Publication No. 2002076635), and the like). However, when a toner comprising a composite oxide is used in a printing device with linear speed exceeding 370 mm/sec, or used for printing on a thick paper having a basis weight exceeding 80 g/m2, fixing failure is generated.
An object of the present invention is to provide a toner which has an excellent fixing ability and gives high-quality fixed images, even when the toner is fixed with a high-speed machine, or fixed on a thick paper.
These and other objects of the present invention will be apparent from the following description.